1. Field
The present application relates to a fuel cell.
2. Description of the Related Art
A typical solid polymer electrolyte fuel cell includes a solid polymer electrolyte membrane formed of a polymer ion exchange membrane. In such a fuel cell, a membrane-electrode assembly (MEA) constituted by a solid polymer electrolyte membrane interposed between an anode and a cathode each constituted by a catalyst layer (electrode catalyst layer) and a gas diffusion layer (porous carbon) is held between separators (bipolar plates). A desired number of such fuel cells are stacked and used as a fuel cell stack for automobile use, for example.
In some MEA, one of the gas diffusion layers of a MEA is designed to have a smaller planar size than that of the solid polymer electrolyte membrane while the other gas diffusion layer is designed to have a planar size smaller than or the same as that of the solid polymer electrolyte membrane but larger than that of the one gas diffusion layer. This type of MEA is known as a step MEA.
For example, a fuel cell disclosed in Japanese Unexamined Patent Application Publication No. 2002-270202 includes an electrode structure 1 interposed between a first separator 2 and a second separator 3, as shown in FIG. 12. An outer sealing member 4a that surrounds the outer periphery of the electrode structure 1 hermetically seals the gap between the first separator 2 and the second separator 3 and an inner sealing member 4b hermetically seals the gap between the second separator 3 and the outer periphery of the electrode structure 1.
The electrode structure 1 includes a solid polymer electrolyte membrane 5, and an anode 6 and a cathode 7 respectively disposed on two sides of the solid polymer electrolyte membrane 5. For example, the electrolyte membrane 5 is oblong in shape and has the same size as the anode 6 disposed on one side. The cathode 7 is designed to have a surface area smaller than that of the anode 6.